/*

* jdatasrc.c

*

* Copyright (C) 1994-1996, Thomas G. Lane.

* Modified 2009-2015 by Guido Vollbeding.

* This file is part of the Independent JPEG Group's software.

* For conditions of distribution and use, see the accompanying README file.

*

* This file contains decompression data source routines for the case of

* reading JPEG data from memory or from a file (or any stdio stream).

* While these routines are sufficient for most applications,

* some will want to use a different source manager.

* IMPORTANT: we assume that fread() will correctly transcribe an array of

* JOCTETs from 8-bit-wide elements on external storage. If char is wider

* than 8 bits on your machine, you may need to do some tweaking.

*/

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */

#include "jinclude.h"

#include "jpeglib.h"

#include "jerror.h"

/* Expanded data source object for stdio input */

typedef struct {

struct jpeg_source_mgr pub; /* public fields */

FILE * infile; /* source stream */

JOCTET * buffer; /* start of buffer */

boolean start_of_file; /* have we gotten any data yet? */

} my_source_mgr;

typedef my_source_mgr * my_src_ptr;

#define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */

/*

* Initialize source --- called by jpeg_read_header

* before any data is actually read.

*/

METHODDEF(void)

init_source (j_decompress_ptr cinfo)

{

my_src_ptr src = (my_src_ptr) cinfo->src;

/* We reset the empty-input-file flag for each image,

* but we don't clear the input buffer.

* This is correct behavior for reading a series of images from one source.

*/

src->start_of_file = TRUE;

}

METHODDEF(void)

init_mem_source (j_decompress_ptr cinfo)

{

/* no work necessary here */

}

/*

* Fill the input buffer --- called whenever buffer is emptied.

*

* In typical applications, this should read fresh data into the buffer

* (ignoring the current state of next_input_byte & bytes_in_buffer),

* reset the pointer & count to the start of the buffer, and return TRUE

* indicating that the buffer has been reloaded. It is not necessary to

* fill the buffer entirely, only to obtain at least one more byte.

*

* There is no such thing as an EOF return. If the end of the file has been

* reached, the routine has a choice of ERREXIT() or inserting fake data into

* the buffer. In most cases, generating a warning message and inserting a

* fake EOI marker is the best course of action --- this will allow the

* decompressor to output however much of the image is there. However,

* the resulting error message is misleading if the real problem is an empty

* input file, so we handle that case specially.

*

* In applications that need to be able to suspend compression due to input

* not being available yet, a FALSE return indicates that no more data can be

* obtained right now, but more may be forthcoming later. In this situation,

* the decompressor will return to its caller (with an indication of the

* number of scanlines it has read, if any). The application should resume

* decompression after it has loaded more data into the input buffer. Note

* that there are substantial restrictions on the use of suspension --- see

* the documentation.

*

* When suspending, the decompressor will back up to a convenient restart point

* (typically the start of the current MCU). next_input_byte & bytes_in_buffer

* indicate where the restart point will be if the current call returns FALSE.

* Data beyond this point must be rescanned after resumption, so move it to

* the front of the buffer rather than discarding it.

*/

METHODDEF(boolean)

fill_input_buffer (j_decompress_ptr cinfo)

{

my_src_ptr src = (my_src_ptr) cinfo->src;

size_t nbytes;

nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);

if (nbytes <= 0) {

if (src->start_of_file) /* Treat empty input file as fatal error */

ERREXIT(cinfo, JERR_INPUT_EMPTY);

WARNMS(cinfo, JWRN_JPEG_EOF);

/* Insert a fake EOI marker */

src->buffer[0] = (JOCTET) 0xFF;

src->buffer[1] = (JOCTET) JPEG_EOI;

nbytes = 2;

}

src->pub.next_input_byte = src->buffer;

src->pub.bytes_in_buffer = nbytes;

src->start_of_file = FALSE;

return TRUE;

}

METHODDEF(boolean)

fill_mem_input_buffer (j_decompress_ptr cinfo)

{

static const JOCTET mybuffer[4] = {

(JOCTET) 0xFF, (JOCTET) JPEG_EOI, 0, 0

};

/* The whole JPEG data is expected to reside in the supplied memory

* buffer, so any request for more data beyond the given buffer size

* is treated as an error.

*/

WARNMS(cinfo, JWRN_JPEG_EOF);

/* Insert a fake EOI marker */

cinfo->src->next_input_byte = mybuffer;

cinfo->src->bytes_in_buffer = 2;

return TRUE;

}

/*

* Skip data --- used to skip over a potentially large amount of

* uninteresting data (such as an APPn marker).

*

* Writers of suspendable-input applications must note that skip_input_data

* is not granted the right to give a suspension return. If the skip extends

* beyond the data currently in the buffer, the buffer can be marked empty so

* that the next read will cause a fill_input_buffer call that can suspend.

* Arranging for additional bytes to be discarded before reloading the input

* buffer is the application writer's problem.

*/

METHODDEF(void)

skip_input_data (j_decompress_ptr cinfo, long num_bytes)

{

struct jpeg_source_mgr * src = cinfo->src;

/* Just a dumb implementation for now. Could use fseek() except

* it doesn't work on pipes. Not clear that being smart is worth

* any trouble anyway --- large skips are infrequent.

*/

if (num_bytes > 0) {

while (num_bytes > (long) src->bytes_in_buffer) {

num_bytes -= (long) src->bytes_in_buffer;

(void) (*src->fill_input_buffer) (cinfo);

/* note we assume that fill_input_buffer will never return FALSE,

* so suspension need not be handled.

*/

}

src->next_input_byte += (size_t) num_bytes;

src->bytes_in_buffer -= (size_t) num_bytes;

}

}

/*

* An additional method that can be provided by data source modules is the

* resync_to_restart method for error recovery in the presence of RST markers.

* For the moment, this source module just uses the default resync method

* provided by the JPEG library. That method assumes that no backtracking

* is possible.

*/

/*

* Terminate source --- called by jpeg_finish_decompress

* after all data has been read. Often a no-op.

*

* NB: *not* called by jpeg_abort or jpeg_destroy; surrounding

* application must deal with any cleanup that should happen even

* for error exit.

*/

METHODDEF(void)

term_source (j_decompress_ptr cinfo)

{

/* no work necessary here */

}

/*

* Prepare for input from a stdio stream.

* The caller must have already opened the stream, and is responsible

* for closing it after finishing decompression.

*/

GLOBAL(void)

jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)

{

my_src_ptr src;

/* The source object and input buffer are made permanent so that a series

* of JPEG images can be read from the same file by calling jpeg_stdio_src

* only before the first one. (If we discarded the buffer at the end of

* one image, we'd likely lose the start of the next one.)

* This makes it unsafe to use this manager and a different source

* manager serially with the same JPEG object. Caveat programmer.

*/

if (cinfo->src == NULL) { /* first time for this JPEG object? */

cinfo->src = (struct jpeg_source_mgr *)

(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,

SIZEOF(my_source_mgr));

src = (my_src_ptr) cinfo->src;

src->buffer = (JOCTET *)

(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,

INPUT_BUF_SIZE * SIZEOF(JOCTET));

}

src = (my_src_ptr) cinfo->src;

src->pub.init_source = init_source;

src->pub.fill_input_buffer = fill_input_buffer;

src->pub.skip_input_data = skip_input_data;

src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */

src->pub.term_source = term_source;

src->infile = infile;

src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */

src->pub.next_input_byte = NULL; /* until buffer loaded */

}

/*

* Prepare for input from a supplied memory buffer.

* The buffer must contain the whole JPEG data.

*/

GLOBAL(void)

jpeg_mem_src (j_decompress_ptr cinfo,

const unsigned char * inbuffer, unsigned long insize)

{

struct jpeg_source_mgr * src;

if (inbuffer == NULL || insize == 0) /* Treat empty input as fatal error */

ERREXIT(cinfo, JERR_INPUT_EMPTY);

/* The source object is made permanent so that a series of JPEG images

* can be read from the same buffer by calling jpeg_mem_src only before

* the first one.

*/

if (cinfo->src == NULL) { /* first time for this JPEG object? */

cinfo->src = (struct jpeg_source_mgr *)

(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,

SIZEOF(struct jpeg_source_mgr));

}

src = cinfo->src;

src->init_source = init_mem_source;

src->fill_input_buffer = fill_mem_input_buffer;

src->skip_input_data = skip_input_data;

src->resync_to_restart = jpeg_resync_to_restart; /* use default method */

src->term_source = term_source;

src->bytes_in_buffer = (size_t) insize;

src->next_input_byte = (const JOCTET *) inbuffer;

}